Multituberculata

Long ago, many mammals lived on Earth.

These animals were like mice or squirrels. Some were very small. Others were big like a beaver.

They had many bumps on their teeth. They used these teeth to eat. They liked seeds and nuts. They also ate fruit and bugs.

Some lived in holes in the ground. Others lived in trees. One kind could climb down trees head first.

These mammals lived for a very long time. They are now gone from the world.

Long ago, a group of mammals called multituberculates lived on Earth.

They lived for over 130 million years. This group lasted longer than any other mammal group. Some were as small as mice. Others were big like beavers.

These animals had very special teeth. Their name comes from the many small bumps, or tubercles, on their teeth. They had large, blade-like teeth in their lower jaw. They used these teeth to slice food. They likely ate seeds, nuts, and fruit. Some may have even eaten worms or insects.

Multituberculates lived in many ways. Some lived in holes in the ground. Others lived in trees. One kind, called Ptilodus, could climb down trees head first. They had toes that could move like a squirrel's.

They lived through the time of the dinosaurs. They reached their peak number of species in the early Paleocene. Later, they faced competition from new mammals like rodents. This led to their decline. They finally went extinct in the late Eocene.

Multituberculates were a very successful group of extinct mammals.

They lived on Earth for over 130 million years. This is a longer time than any other group of mammal-like creatures. They first appeared during the Middle Jurassic period. They were very diverse, with more than 200 different species known to scientists. These animals came in many different sizes. Some were tiny like mice. Others were large, like the taeniolabids which were as big as beavers.

These mammals had a very special way of eating. Their name comes from the many small bumps on their teeth, called tubercles. They had large, blade-like teeth in their lower jaw called premolars. They used these teeth to slice through food. To chew, they used a unique jaw movement. Instead of moving side-to-side like we do, they moved their jaws from front to back. This is called a palinal jaw stroke. First, they sliced food with their blade-like teeth. Then, they used their back teeth to grind the food.

Scientists have studied these fossils to learn about their history. The earliest multituberculates were found in England and Russia. These early forms lived during the Middle Jurassic, about 166 to 168 million years ago. One group was called Plagiaulacida, which included more primitive members. Later, a more advanced group called Cimolodonta appeared in North America. By the Late Cretaceous, Cimolodonta became the main type of multituberculate. They were very widespread across much of the land known as Laurasia.

These animals lived in many different places. Some lived in burrows under the ground. Others were like squirrels and lived in trees. The Ptilodus lived in North America and was very good at climbing. They had special toes that could move in many directions. This let them climb down trees head first, just like modern squirrels.

Other types, like the taeniolabids, were heavy and lived on the ground. Some multituberculates also lived in the Southern Hemisphere. Fossil remains have been found in Australia and Madagascar. Even some fossils in South America might be multituberculates.

Multituberculates were very common for a long time. They reached their highest number of species during the early Paleocene. This was right after a major extinction event. However, they eventually began to decline. They had to compete with new mammals like rodents and ungulates. These newer mammals were very good at finding food. Because of this competition, the multituberculates slowly disappeared. The last of them went extinct during the Late Eocene.

Multituberculata was an extinct order of rodent-like mammals.

They were incredibly successful, lasting over 130 million years. This period is longer than any other order of mammaliforms. They first appeared during the Middle Jurassic period. They reached a peak in diversity during the Late Cretaceous and Paleocene. Eventually, they declined and went extinct in the Late Eocene. Scientists have identified more than 200 different species. These animals varied greatly in size. Some were as small as mice. Others, like the taeniolabids, were as large as beavers.

The name multituberculate refers to the many small bumps on their teeth. These bumps are called tubercles. Their dental anatomy was somewhat similar to modern rodents. They had chisel-like front teeth. A wide, toothless gap called a diasteme separated these from their cheek-teeth. The cheek-teeth featured several rows of tubercles. These rows worked against similar rows in the jaw. Unlike rodents, which have teeth that grow continuously, multituberculates used dental replacement. This is the process where new teeth replace old ones. Most species followed typical mammalian patterns. However, some species had lower incisors that erupted long after the root closed.

A defining feature was a massive fourth lower premolar. This tooth is called a plagiaulacoid. In some earlier multituberculates, the first three lower premolars were all plagiaulacoids. These teeth increased in size toward the back of the jaw. In the Cimolodonta subgroup, only the fourth premolar remained large. The third premolar became a small, vestigial peg. In some taxa, like the taeniolabidoideans, the plagiaulacoid disappeared or became a molariform tooth.

This tooth had a serrated, blade-like edge. It was likely used for slicing through tough food like seeds or nuts.

Multituberculates used a unique way to chew. Most modern mammals use a side-to-side or front-to-back jaw movement. Multituberculates used a palinal jaw stroke. This means the jaw moved from the front toward the back. This movement required very different jaw muscles and tooth shapes. Their eating process likely happened in two distinct stages. First, the last upper premolar held the food in place. Then, the blade-like lower premolars sliced the food as the jaw moved upward. Finally, the lower jaw moved backward to grind the food between the molar rows.

The evolutionary history of this group is long and complex. The earliest known fossils come from the Middle Jurassic. These include *Hahnotherium* and *Kermackodon* from England. They also include *Tashtykia* and *Tagaria* from Russia. These early forms are known mostly from isolated teeth. Scientists group early multituberculates into a group called Plagiaulacida. This group is considered paraphyletic, meaning it is a primitive evolutionary grade. Later, the more advanced Cimolodonta appeared in North America during the Early Cretaceous. By the early Late Cretaceous, Cimolodonta had replaced the older lineages.

These mammals occupied many different ecological niches. Some were burrow-dwellers. Others lived in trees, much like modern squirrels. The genus *Ptilodus* is a great example of an arboreal species.

Fossils from the Bighorn Basin show they had highly mobile big toes. They could move their toes to grip branches. This allowed them to climb down trees head-first. Other groups, like the taeniolabids, were heavy and lived on the ground. They were built for a terrestrial life. Some multituberculates even lived in the Southern Hemisphere. Fossil evidence exists from Australia and Madagascar. Some fossils in South America might also belong to this group.

Multituberculates are classified within a group called Allotheria. This group also includes Euharamiyida and Gondwanatheria. The exact placement of these groups is often debated by scientists. Some studies suggest multituberculates are closely related to the crown mammals. Crown mammals include placentals, marsupials, and monotremes. However, recent findings place Allotheria outside the crown group of Mammalia. This suggests that certain traits, like live birth, may have evolved independently.

This complex history shows how diverse and adaptable these mammals truly were.